Furnace tunnels and assembly system

ABSTRACT

Flue gas entry into the tunnel(s) of a furnace is controlled by openings through the entry ports. A furnace tunnel assembly system uses interlocking refractory blocks to form a longitudinal wall of a flue gas flow channel in a firebox. Plugs in some of the ports inhibit flue gas entry from the firebox to the flow channel, and flow passages in some of the ports allow the flue gas to enter the flow channel from the firebox. The flow passages can be provided as inserts having orifices of varying diameter and a profile matching the ports in which they are placed. Matching the flow conductivity (or cross-sectional flow area) and pressure drop through the individual ports to the desired mass flow, the flue gas flow can be distributed evenly, or as otherwise desired, into different ports, intervals, and/or regions of the tunnel.

RELATED APPLICATIONS

This application is a continuation of co-pending U.S. Ser. No.15/532,029, filed May 31, 2017, now U.S. Pat. No. 10,458,707, which is anational stage entry of PCT/US2016/053876, Sep. 27, 2016, which is anonprovisional of and claims priority benefit of U.S. 62/233,931 filedSep. 28, 2015.

FIELD OF THE INVENTION

The present invention relates to furnace flue gas tunnels and relatedmethods.

BACKGROUND

Fired heaters or furnaces, herein used interchangeably, are commonelements of industrial plants. With reference to the reformer furnace Rillustrated in FIG. 1, a section F (or sections) typically referred toas the radiant section or firebox contains a means of oxidizing fuel torelease heat and reaction products (“flue gas” or “exhaust gas”). Thisis commonly achieved by combustion of fuel and air using industrialburners B, and in the case of heating and/or reacting fluids, theradiant section F contains a plurality of tubes T to heat the fluids.

Furnaces include reformers, steam crackers, other reactors, andnon-reactive heaters employing burners or other oxidative methods ofgenerating heat and creating flue gas. As used herein, flue gasencompasses any combination of combustion products or effluent gas.

Whether the radiant section F is used for reacting components or merelyfor heating, the flue gas is gathered in a series of longitudinaltunnels 1 including opposite outside row tunnels 2 and one or moreinside row tunnels 4, and passed through transition section 6 toconvection section 8, which is a heat recovery section dominated byconvective heat transfer where additional heat is often recovered fromthe flue gas.

With reference to some additional details shown in FIGS. 2 and 3, theflue gas flows into the tunnels 1 through uniformly sized openings orports 10 spaced along the length of the tunnels, and exits from the openends 12 into the transition section 6 and/or convection section 8, orother downstream flue gas processing equipment.

The tunnels 1 may include a pair of side walls 16 in each inside tunnel,or a side wall 18 in the case of an outside tunnel, and an outer wall 20against the firebox wall 22 in the case of the outside row tunnels 2,which are erected from the furnace floor 24 using insulating firebrickstransitioning to regular firebrick secured with mortar up to a roof orlid 26, sometimes called coffin covers, often made from large refractoryslabs with large expansion gaps created at regular intervals to accountfor thermal expansion.

The tunnels 1 have flow channels for the flue gas which are normally ofuniform width, height and cross-sectional area between the open end 12and closed end 14. To balance the amount of flue gas entering thetunnels 1 at various points along their length, the number of openingsor ports 10 per interval is decreased relative to the pressure dropthrough the ports 10, which due to the velocity of the flue gas in thetunnels 1, usually means that the number of holes is decreased relativeto the distance of the interval from the closed end 14 of the tunnel 1,or stated another way, increased relative to the distance of theinterval from the exit end 12 of the tunnel. The ports 10 are formed asthe walls 16, 18 are constructed by leaving out half blocks in regularpatterns. Since the outside row tunnels 2 generally receive flue gasfrom the outside row of burners from one side only, these tunnels areusually sized to receive only a fraction of the flue gas passing throughthe inside row tunnels 4, e.g., 65%. An example applying the industrystandard design principles for flue gas tunnels is presented in Table 1.

From this example, it is seen that the use of uniform opening sizes onlyallows a rough approximation of the desired opening area in eachinterval. Furthermore, because of the high temperature and thermalstresses, the tunnels 1 are usually constructed with pilasters in thewalls at regular intervals 28, which do not allow the placement ofopenings using conventional block construction techniques. The placementof ports 10 in the industry standard tunnel design thus usually resultsin a very uneven, fluctuating entry or mass flow rate of flue gas alongthe various intervals, as shown in FIG. 4. Moreover, the ports 10 arenormally positioned near or upwardly from the bottom of the tunnels 1,so that there is greater flue gas flow at the bottom of the tubes Tespecially where they are more vulnerable to these excessive temperaturefluctuations. While heating in the firebox F is dominated by radiance,the temperature fluctuations can be sufficiently substantial, especiallyduring startup and/or shutdown, to eventually result in premature tubefailure and loss of the flow of reactants through the failed tubes,which in turn further exacerbating the temperature fluctuations.

TABLE 1 Example of Flue Gas Tunnel Design Principles* Property ClosedEnd Midpoint Open End Inside Tunnel Velocity, m/s (ft/sec)  0 15 (50)  30 (100) Total Gauge Pressure, Pa (in. w.c.) −187 (−0.75) −189 (−0.76)−194 (−0.78) Velocity Pressure, Pa (in. w.c.)  0  72 (0.29) 291 (1.17)Static Gauge Pressure, Pa (in. w.c.) −187 (−0.75) −261 (−1.06) −490(−1.95) Firebox Gauge Pressure, Pa (in. w.c.) −150 (−0.60) −150 (−0.60)−150 (−0.60) Differential Pressure, Pa (in. w.c.)  37 (0.15) 114 (0.46)336 (1.35) Calculated Relative Opening Area 10 5.7 3.4 (dimensionless)Actual Relative Opening Area Due 10 6   3   to Rounding to Number ofOpenings *From BD Energy Systems Steam Methane Reformer AdvancedTraining Course Handbook, Part 2 - Critical Design Features, Chapter 4 -Radiant Section (2015). Based on tunnels of uniform cross-sectional flowarea.

Other efforts to make the flow of flue gas into the tunnels more uniformhave included angled slots in the lid of the tunnel and an increasingcross-sectional area of the tunnel to maintain a uniform velocity offlue gas in the tunnel, as described in US 2007/0234974 A1. Additionaldesign parameters and issues are described in BD Energy Systems SteamMethane Reformer Advanced Training Course Handbook, Part 2—CriticalDesign Features, Chapter 4—Radiant Section (2015).

Recently, stackable, interlocking refractory blocks made with mulliteand/or alumina resistant to high temperature creep, have been madeavailable to the industry, such as those described in US 2006/0242914A1; or those described in J. Quntiliana et al., “Improving Flue GasTunnel Reliability, Nitrogen+Syngas, No. 336, p. 59 (July-August 2015),and WO 2015/188030, e.g., the STABLOX™ flue gas tunnel systemcommercialized by Blasch Precision Ceramics (Albany, N.Y.). The use ofthese tunnel systems has facilitated a more versatile location of theports 10, as well as a more stable and quicker tunnel wall construction.Even so, optimizing the industry standard tunnel design for more preciseplacement of uniformly sized ports 10, still results in a significantvariation in flue gas mass flow rates, e.g., as seen in the example ofFIG. 5.

The industry would benefit from improved flue gas tunnel designs andoperations that avoid or lessen the extent of drawbacks associated withthe fluctuation of flue gas flow into and/or within the flue gastunnels.

SUMMARY OF THE INVENTION

In one aspect of the invention, embodiments provided herein are directedto a furnace tunnel assembly system, comprising a plurality ofinterlocking refractory blocks adapted to form a longitudinal wall of aflue gas flow channel in a firebox, at least some of the blockscomprising ports integrally formed therein, wherein the ports arearranged in regular rows and columns, and inserts for the ports, whereinat least some of the inserts comprise plugs comprising imperforateplates having a profile matching the ports to inhibit flue gas entryfrom the firebox to the flow channel, and wherein at least some of theports comprise flow passages for the flue gas to enter the flow channelfrom the firebox.

In another aspect of the invention, a furnace tunnel assembly systemcomprises a plurality of interlocking refractory blocks adapted to forma longitudinal wall of a flue gas flow channel in a firebox, at leastsome of the blocks comprising ports formed therein, wherein the portsare arranged in regular rows and columns, and respective inserts for theports, wherein at least some of the inserts comprise plugs comprisingimperforate plates, and wherein some of the inserts comprise perforatedplates.

In another aspect of the invention, a furnace comprises a firebox and afurnace tunnel assembled from the furnace tunnel assembly system.

In another aspect of the invention, a method comprises assembling afurnace tunnel from the blocks, plugs, flow passages, and/or perforatedinserts of the furnace tunnel assembly system.

In another aspect of the invention, a method comprises positioning aplurality of interlocking refractory blocks to form a longitudinal wallof a flue gas flow channel in a firebox, wherein at least some of theblocks comprising ports integrally formed therein, arranging the portsin regular rows and columns, plugging some of the ports with plugscomprising imperforate plates having a profile matching the ports toinhibit flue gas entry from the firebox to the flow channel; andproviding some of the ports with flow passages for the flue gas to enterthe flow channel from the firebox.

In one or more embodiments of the invention, the entry of the flue gasinto the tunnel(s) of a furnace is controlled by providing a uniform orregular spacing of entry ports along a tunnel structure, such as awall(s) and/or roof, and varying the flow conductivity among the entryports. In some embodiments the flow conductivity is controlled by thesize of a passage through the port, e.g., diameter, which may beprovided either as through bores of varying diameter or otherwiseintegrally formed in the structure, or as inserts having bores ofvarying diameter which are placed in ports having a uniform size. Insome embodiments, by matching the flow conductivity and pressure dropthrough the individual ports (or groups or intervals) to the desiredmass flow, the flue gas can be distributed as desired to differentlocations or regions of the tunnel, e.g., to achieve an essentiallyevenly distributed mass flow into the tunnel at longitudinal intervals,such as by increasing the diameter of the passages from smallest in theinterval near the open or exit end of the tunnel to largest in theinterval farthest from the open end, e.g., adjacent a closed end of thetunnel, especially where the tunnel has a uniform cross-sectional area.In an embodiment of the invention, a furnace tunnel, defining a flowchannel for flue gas from a firebox to pass to an open end of thetunnel, comprises a longitudinal refractory structure separating theflow channel from the firebox, a plurality of ports formed in therefractory structure for the flue gas to enter the flow channel from thefirebox, a regular spacing pattern of the ports along the length of therefractory structure, and a passage through each of the respective portsproviding relatively varied flow conductivities to control flue gasentry into the flow channel.

In another embodiment, a furnace comprises a firebox, and one or moretunnels defining a flow channel for flue gas from a firebox to pass toan open end of the tunnel, and comprising a longitudinal refractorystructure separating the flow channel from the firebox, a plurality ofports formed in the refractory structure for the flue gas to enter theflow channel from the firebox, a regular spacing pattern of the portsalong the length of the refractory structure, and a passage through eachof the respective ports providing relatively varied flow conductivitiesto control flue gas entry into the flow channel.

In other embodiments of the invention, a furnace tunnel assembly systemcomprises a plurality of interlocking refractory blocks adapted to forma longitudinal wall of a flue gas flow channel in a firebox, at leastsome of the blocks comprising ports formed for the flue gas to enter theflow channel from the firebox, and respective flow passages for theports, wherein at least some of the ports comprise passages having arelatively different flow conductivity than at least some of the otherpassages.

In other embodiments, a method comprises stacking refractory blocks toform a longitudinal wall of a furnace tunnel, providing a uniformdensity of ports in successive intervals in the wall between open andclosed ends of the tunnel, and providing flow passages of varyingrelative flow conductivity through the ports.

In other embodiments, a method comprises passing flue gas from a fireboxthrough a longitudinal refractory structure of a tunnel, positioningpassages in respective ports evenly distributed along the length of therefractory structure to admit the flue gas into a flow channel in thetunnel, and controlling relative flow rates of the flue gas through theports by providing some of the passages with a different flowconductivity relative to the other passages, e.g., differentcross-sectional areas or diameters.

In other embodiments, a flue gas tunnel comprises a longitudinal wallextending along a flow channel from a closed end of the tunnel to anopen end of the tunnel; a plurality of ports of uniform profile formedin the wall for the flue gas to enter the flow channel and arranged incolumns from a near column adjacent the open end to a far columnadjacent the closed end and a plurality of intermediate columns betweenthe near and far columns, wherein each of the columns has the samenumber of ports; a like plurality of inserts having a profile matchingthe respective ports and received therein; orifices formed in therespective inserts; a plurality of sets of the inserts, each set havinga different orifice diameter with respect to the other sets, each set ofinserts comprising orifices of uniform diameter within the set; whereineach column comprises a plurality of inserts selected from one or moreof the sets of inserts, such that an overall cross-sectional flow areathrough the orifices of each column increases from the near column tothe far column.

In other embodiments, a flue gas tunnel disposed in a fired heatercomprises a floor, two side walls, a roof, and one or two open endsthrough which flue gas may exit, optionally through a respectivetransition section(s), into a respective convection section(s) which maybe a common convection section or separate convection sections. At leastone side all comprises a plurality of passages of varyingcross-sectional areas.

In some embodiments, a plurality of any of the flue gas tunnelsdescribed herein are disposed in a steam-methane reformer firebox, thetunnels having an open end through which flue gas may exit into a commonconvection section or separate convection sections, or through atransition section and into the common convection section. In someembodiments, the plurality of tunnels comprises outer tunnels having onewall with the ports and/or passages formed therein, and inner tunnelsbetween the outer tunnels, the inner tunnels having a pair of opposingside walls with the ports and/or passages formed therein.

In some embodiments, the ports in the refractory structure are equippedwith directional flow diverters to promote mixing of the flue gas in thetunnel with a reactant introduced into the tunnel, e.g., a reducingagent to promote selective non-catalytic reduction of the NOxcomponents.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional perspective view showing the layout of a typicalsteam-methane reformer furnace.

FIG. 2 is a side elevation view of the typical brick construction usedfor a side wall of a flue gas tunnel according to the prior art.

FIG. 3 is an end cross-sectional elevation view of a typical tunnelsection of a reformer furnace as seen along the view lines 3-3 of FIG.2.

FIG. 4 is a graph of the mass flow distribution along intervals ofconventional tunnels employing a typical industry standard design.

FIG. 5 is a graph of the mass flow distribution along intervals ofconventional tunnels employing an optimized industry standard design.

FIG. 6 is sectional perspective view showing the layout of a steammethane reformer furnace according to some embodiments of the presentinvention.

FIG. 7 is a side elevation view of a ported side wall of a flue gastunnel according to some embodiments.

FIG. 8 is a graph of the mass flow distribution along intervals ofported tunnels according to some embodiments of the present invention.

FIG. 9 is a side view of a portion of a ported tunnel wall having flowpassages formed between blocks according to some embodiments of thepresent invention.

FIG. 10 is a side view of a portion of a ported tunnel wall havingintegral flow passages according to some embodiments of the presentinvention.

FIG. 11 is a side view of a portion of a ported tunnel wall having flowpassage inserts according to some embodiments of the present invention.

FIG. 12 is a side view of a portion of a ported tunnel wall having flowpassage inserts according to some other embodiments of the presentinvention.

FIG. 13 is a side view of a portion of a ported tunnel wall having flowpassage inserts according to some other embodiments of the presentinvention.

FIG. 14 is a side view of a portion of a ported tunnel wall having flowpassage inserts according to some other embodiments of the presentinvention.

FIG. 15A is a side view of a portion of a ported tunnel wall having flowpassage inserts according to some other embodiments of the presentinvention.

FIG. 15B is a side view of a portion of the ported tunnel wall of FIG.15B having flow passage inserts and plugs according to some otherembodiments of the present invention.

FIG. 15C is a perspective view of an interlocking block used in thetunnel walls of FIGS. 15A-15B.

FIG. 15D is a side view of the stacked blocks of FIG. 15C.

FIG. 16A is a schematic illustration of a tunnel flow pattern accordingto some embodiments of the present invention.

FIG. 16B is a schematic illustration of another tunnel flow patternaccording to some embodiments of the present invention.

FIG. 17 is a perspective view of a directional flow diverter accordingto some embodiments of the present invention.

FIG. 18A is a schematic diagram showing an example of the orifice layoutin intervals 1-26 from the closed end (left) of a tunnel designaccording to some embodiments of the present invention.

FIG. 18B is a schematic diagram showing the orifice layout in intervals27-56 approaching the open end (right) of the tunnel design of FIG. 18Aaccording to some embodiments of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions are applicable herein:

Adapted to—made suitable for a use or purpose; modified.

Adjacent—next to or adjoining.

Block (brick)—a large solid or hollow piece of hard material, especiallyrock, stone, concrete, refractory, or wood, typically rectangular withflat surfaces on each side.

Channel—a passage or duct for fluid.

Columns—a vertical or upright arrangement of items.

Closed—having or forming a boundary or barrier.

Control—determine the behavior or supervise the running of.

Cross-sectional area—the extent or measurement of a surface or shapethat is or would be exposed by making a straight cut through something,especially at right angles to an axis.

Diameter—a straight line passing from side to side through the center ofa body or figure, especially a circle or sphere; the radius is half thediameter.

Different—not the same as another or each other; unlike in nature, form,or quality.

Disposing—putting or arranging in a particular place or way. Usedsynonymously with placing and positioning.

Dividing—physically or, for the purposes of design, conceptuallyseparating into parts.

Each—used to refer to every one of two or more things, regarded andidentified separately.

Embodiments—non-limiting tangible or visible forms of an idea or qualityaccording to the present disclosure or invention.

End—the furthest or most extreme part or point of something.

Enter—come or go into.

Entry—the act of going or coming in.

Far—at, to, or by a great distance (used to indicate the extent to whichone thing is distant from another).

Firebox—the chamber of a furnace or boiler in which fuel is burned.

Floor—the lower inside surface of a hollow structure.

Flow—to issue or move in a stream.

Flow conductivity—a measure of how easily a given fluid moves through achannel, passage or orifice at a given pressure drop; the inverse offlow resistivity; the value of K in the equation Q/A=−K*(dp/dx) whereQ/A is the superficial or Darcy's velocity (where Q is the volumetricflowrate of the fluid and A is the geometric cross-sectional area of theflow passage or medium), and dp/dx is the pressure change per unitlength of the flow passage. For circular orifices the flow conductivityis proportional to the cross-sectional flow area or diameter squared. Ifthe relative flow conductivity of two passages is different depending onthe fluid properties and/or flow conditions, the relative flowconductivities are determined using the fluid and conditions actuallypresent, or if the fluid and conditions are not specified, using a fluegas comprised of 1.7 mol % O₂, 7.8 mol % CO₂, 20 mol % H₂O, and 70.5 mol% N₂ at entry conditions of 101.2 kPa and 1050° C. (1904° F.), and apressure drop of 100 Pa (0.4 in. water).

Flue gas—the mixture of gases resulting from combustion and otherreactions in a furnace.

Furnace—a structure or apparatus in which heat may be generated at veryhigh temperatures.

Hydraulic diameter—DH=4A/P, where DH is the hydraulic diameter, A is thecross sectional area and P is the wetted perimeter of a channel, duct,or passage.

Essentially imperforate—having no significant openings or apertures.

Insert—a thing that is placed or fit into another thing.

Interlocking—engaging with each other by overlapping or by fittingtogether projections and recesses.

Intermediate—coming between two things in time, place, order, character,etc.

Interval—a space between two objects, points or units.

Length—measurement or extent of something along its greatest dimension.

Longitudinal—running or along the length of a body; pertaining orextending along the long axis of a body.

Near—located a short distance away.

Open—allowing access, passage, or a view through an empty space; notclosed or blocked up.

Pass—move or cause to move in a specified direction.

Passage—a path, channel, or duct through, over, or along which somethingmay pass.

Plate—a thin, flat sheet or strip of metal or other material, typicallyone used to join or strengthen things or forming part of a machine; apanel.

Plurality—two or more.

Port—an aperture or opening.

Refractory—a substance or material that is resistant to heat.

Regular—arranged in or constituting a constant or definite pattern,especially with the same space between individual instances.

Respective—belonging or relating separately to each of two or morepeople or things.

Roof or lid—a structure forming an upper cover.

Rows—a number of things in a more or less straight line Separate—divideor cause to divide into constituent or distinct elements.

Set—a group or collection of similar things.

Size—the relative extent of something.

Spacing—the arranging of the distance between things.

Spacing pattern—a regular arrangement of the distance between things.

Square pattern—a pattern in which joining the centers of four adjacentitems forms a square.

Structure—a building or other object constructed from several parts.

Successive—following one another or following others.

Through—moving or lying in one side and out the other.

Triangular pattern—a pattern in which joining the centers of threeadjacent items forms an oblique triangle (without a right angle).

Tunnel—a covered passageway, e.g., a structure physically defining aflow channel for flue gas to exit from a furnace.

Uniform—of the same form, manner, degree or character.

Upright—vertical or erect.

Varied—incorporating a number of different types or elements; showingvariation or variety.

Wall—a structure enclosing or shutting off a space.

In some embodiments of the invention, a furnace tunnel defines a flowchannel for flue gas from a firebox to pass to an open end of thetunnel, e.g., a tunnel having a constant or uniform cross-sectional flowarea. In some embodiments, the tunnel comprises a longitudinalrefractory structure separating the flow channel from the firebox, aplurality of ports formed in the refractory structure for the flue gasto enter the flow channel from the firebox, a regular spacing pattern ofthe ports along the length of the refractory structure, and a passagethrough each of the respective ports providing relatively varied flowconductivities to control flue gas entry into the flow channel.

In some embodiments, the refractory structure comprises at least oneupright wall and a roof, e.g., with the ports in the wall(s) and anessentially imperforate roof. In some embodiments, the flow channel canhave an essentially uniform cross-sectional flow area. In someembodiments, the refractory structure comprises blocks, e.g.,interlocking and/or stackable blocks. In some embodiments, the ports areintegrally formed in the blocks, e.g., by casting or boring, andperforated inserts are received in the ports. In some embodiments, theperforations, e.g., orifices, define cross-sectional flow areas throughthe respective passages. In some embodiments, the ports have a uniformprofile and/or the inserts have a profile matching the respective ports.In some embodiments, the perforations in some of the inserts have across-sectional flow area that is greater with respect to theperforations of some of the other inserts. In some embodiments, theperforated inserts comprise sets of a plurality of the inserts, whereinthe perforations within each set of inserts have a uniformcross-sectional flow area that differs with respect to the other one ormore sets of inserts.

In some embodiments, the ports are disposed in a plurality of intervalscomprising a near interval adjacent to the open end, a far intervalspaced away from the open end, e.g., adjacent to a closed end of thetunnel, and a plurality of intermediate intervals between the near andfar intervals. In some embodiments, the passages through the portsprovide the far interval with an overall flue gas flow conductivityrelatively greater than the overall flue gas flow conductivity of thenear interval. In some embodiments, the overall flue gas flowconductivities of the respective intermediate intervals increasesuccessively from the near interval to the far interval. In someembodiments, the passages through the ports provide the far intervalwith an overall cross sectional flow area greater than the overall crosssectional flow area of the near interval, and/or the overall crosssectional flow area of the respective intermediate intervals increasesuccessively from the near interval to the far interval.

In some embodiments, each of the near, far and intermediate intervalshave the same number of ports. In some embodiments, the ports have auniform profile and receive perforated inserts having a matchingprofile. In some embodiments, the perforated inserts comprise one ormore sets of the inserts having a uniform perforation diameter. In someembodiments, the far interval has an overall cross sectional flow areagreater than the overall cross sectional flow area of the near interval,and/or the overall cross sectional flow area of the respectiveintermediate intervals increases successively from the near interval tothe far interval. In some embodiments, the inserts in each intervalcomprise inserts from a single set of inserts or from a plurality ofdifferent sets.

In some embodiments according to the present invention, a flue gastunnel comprises a longitudinal wall extending along a flow channel froma closed end of the tunnel to an open end of the tunnel; a plurality ofports of uniform profile formed in the wall for the flue gas to enterthe flow channel, and arranged in columns from a near column adjacentthe open end to a far column adjacent the closed end and a plurality ofintermediate columns between the near and far columns, wherein each ofthe columns has the same number of ports; a like plurality of insertshaving a profile matching the respective ports and received therein;orifices formed in the respective inserts; a plurality of sets of theinserts, each set having a different orifice diameter with respect tothe other sets, each set of inserts comprising orifices of uniformdiameter within the set; wherein each column comprises a plurality ofinserts selected from one or more of the sets of inserts, such that anoverall cross-sectional flow area through the orifices of each columnincreases from the near column to the far column.

In some embodiments, the wall comprises interlocking blocks, the portsare arranged in regular rows and columns, and/or the ports are arrangedin a triangular pattern or a square pattern. In some embodiments, thetunnel further comprises single ones of the inserts having a differentorifice diameter than the sets of the inserts in the ports of one ormore of the columns.

In some embodiments of the invention, a furnace tunnel defines a flowchannel for flue gas from a firebox to pass to an open end of thetunnel, and comprises a longitudinal refractory structure separating theflow channel from the firebox, a plurality of ports formed in therefractory structure for the flue gas to enter the flow channel from thefirebox, a regular spacing pattern of the ports along the refractorystructure, and respective passages through the ports having a variedflow conductivity to control flue gas entry into the flow channel.

In some embodiments according to the present invention, a furnacecomprises a firebox and the furnace tunnel of any one or combination ofembodiments described herein.

In some embodiments according to the present invention, a furnace tunnelassembly system comprises a plurality of interlocking refractory blocksadapted to form a longitudinal wall of a flue gas flow channel in afirebox. In some embodiments, at least some of the blocks comprise portsformed for the flue gas to enter the flow channel from the firebox, andthere are respective flow passages for the ports. In some embodiments,at least some of the ports comprise passages having a relativelydifferent flow conductivity than at least some of the other passages.

In some embodiments of the assembly system, the flow passages compriseopenings defined by the profiles of the respective ports, e.g., boresthrough the blocks, and the different flow conductivities correspond todifferent cross-sectional areas of the openings, e.g., diameters of thebores.

In some embodiments of the assembly system, the flow passages compriseone or more perforations or orifices formed in respective insertsreceivable in the ports, e.g., where the different flow conductivitiescorrespond to different cross-sectional areas of the perforations and/ordiameters of the orifices.

In some embodiments, the assembly system comprises a plurality of setsof the port openings or inserts having different perforation or orificesizes, from which the appropriate or most nearly appropriate size can beselected for a particular port location, or combination of sizes for theports in a particular interval. For example, the system can comprise aplurality of sets of the inserts, wherein the inserts within each sethave respective orifices of the same size, and wherein each set hasdifferent orifice sizes than the other sets. In this manner the portopenings (e.g., in prefabricated blocks) or inserts can be manufacturedin an array of different sizes, an inventory thereof transported to theassembly site, and the appropriate size selected from the inventory fora particular port location. In one non-limiting example, the inventoryof port openings and/or inserts can have “standard” sizes to facilitateassembly, e.g., a smallest diameter of from 12.7 mm (0.5 in.) to 19.1 mm(0.75 in.), incremented by 3.17 mm (0.125 in.) up to 31.8 (1.25 in.) to44.4 mm (1.75 in.), and then incremented by 6.35 mm (0.25 in.) up to alargest diameter of from 63.5 mm (2.5 in.) or 76.2 mm (3 in.). In thismanner the wall may be constructed with standard size blocks and/orinserts, selecting the ones with the appropriate opening sizes for thelocation or interval of the wall.

In some embodiments, the assembly system comprises a kit or essentiallycomplete inventory of component parts for the furnace tunnel assembly,and/or a plurality of the component parts partially pre-assembled intoone or more modules.

In some embodiments according to the present invention, a methodcomprises assembling a furnace tunnel from the blocks and/or inserts ofany one or combination of embodiments of the furnace tunnel assemblysystem described herein.

In some embodiments according to the present invention, a methodcomprises stacking refractory blocks to form a longitudinal wall of afurnace tunnel, providing a uniform density of ports in successiveintervals in the wall between open and closed ends of the tunnel, andproviding flow passages of varying relative flow conductivity throughthe respective ports. In some embodiments, the method further comprisesplacing perforated inserts in the ports, wherein the flow passagescomprise one or more orifices formed in respective inserts which areadapted to be received in the ports, and or wherein the different flowconductivities correspond to different diameters of the orifices. Insome embodiments, the method further comprises varying cross-sectionalareas of the passages to regulate entry of flue gas from a firebox intothe tunnel, e.g., such that a mass flow of the flue gas from the fireboxis uniformly distributed through each interval.

In some embodiments according to the present invention, a methodcomprises passing flue gas from a firebox through a longitudinalrefractory structure of a tunnel, positioning passages in respectiveports evenly distributed along the length of the refractory structure toadmit the flue gas into a flow channel in the tunnel, and controllingrelative flow rates of the flue gas through the ports by providing someof the passages with a different flow conductivity relative to the otherpassages.

In some embodiments, the method further comprises dividing (for designpurposes) the length of the refractory structure into a plurality ofregular intervals having the same number of ports, wherein the overallflow conductivity of some of the intervals is different relative to theother intervals, e.g., wherein the overall flow conductivity ofsuccessive intervals increases from a near interval adjacent to an openend of the tunnel to a far interval adjacent a closed end of the tunnel.In some embodiments, the method alternatively or additionally comprisesevenly distributing a mass flow rate of the flue gas entering the tunnelamong the intervals, e.g., such that the mass flow rate of the flue gasthrough each interval is no more than 2% greater or less than an overallaverage of the mass flow rate through the intervals.

In some embodiments, the method further comprises placing inserts inrespective ports, the inserts comprising the respective passages. Insome embodiments, the inserts and ports have matching profiles. In someembodiments the inserts comprise sets of perforated inserts, wherein theperforations within each set of inserts have a uniform cross-sectionalflow area, e.g., diameter, that differs with respect to the other one ormore sets of inserts.

In some embodiments, the method further comprises dividing (for designpurposes) the length of the refractory structure into a plurality ofregular intervals having the same number of ports, wherein the intervalscomprise a near interval adjacent to an open end of the tunnel, a farinterval spaced away from the open end, and a plurality of intermediateintervals between the near and far intervals, wherein the perforationsin the inserts provide the far interval with an overall cross sectionalflow area relatively greater than the overall cross sectional flow areaof the near interval, and wherein the overall cross sectional flow areaof the respective intermediate intervals increase successively from thenear interval to the far interval. In some embodiments, the inserts ineach interval comprise inserts from a single set of inserts or from aplurality of different sets. With reference to FIGS. 6 and 7, an exampleof a longitudinal refractory structure takes the form of an upright orvertical wall 100 disposed between the flow channel and the firebox. Aplurality of ports 102 are formed in the refractory structure 100 forthe flue gas to enter the flow channel from the firebox, for example,using a regular spacing pattern of the ports 102, e.g., in regularlyspaced rows and/or columns. To control flue gas entry into the flowchannel, passages through the ports 102 may have individually selectedflow conductivity, or groups of the ports 102, e.g., by longitudinalinterval, may have a selected overall flow conductivity that varies frominterval to interval depending on the anticipated pressure drop toobtain the desired flow rate, as described below in more detail. In thefollowing discussion, flow conductivity is varied by a varyingcross-sectional area or diameter as one example for the purpose ofclarity and illustration, however, other embodiments for varying flowconductivity such as the length, tortuosity, permeability, etc., of theflow passages, are also applicable to and useful in some embodiments ofthe invention.

By providing the ports 102 in a regular spacing pattern as shown inFIGS. 6-7, and varying the diameter of the through passages, the flowrate of the flue gas through each port 102 can be individuallycontrolled for a given pressure drop and/or other conditions, e.g., toallow more or less flue gas to pass through each port 102 as desired,and/or to allow about the same amount of flue gas to enter through eachport 102 or through each interval of the ports 102 where an even orbalanced passage of flue gas into the tunnel wall 100 and the pressuredifferential may vary. In one exemplary embodiment as shown in FIG. 8,an even or balanced incremental mass flow of flue gas is achieved ineach longitudinal interval along the extent each of the walls 100, e.g.,such that the mass flow rate of the flue gas through each interval is nomore than 2% greater or less than an overall average of the mass flowrate through the intervals, or no more than 1.5% greater or less than anoverall average of the mass flow rate through the intervals, or no morethan 1% greater or less than an overall average of the mass flow ratethrough the intervals.

FIG. 9 shows an arrangement of ports 150 in portions of the wall 152 atthe 3-column, 3-row near interval 158 adjacent an open (exit) end of thetunnel, a similar intermediate interval 156, and a similar far interval154 adjacent a closed end of the tunnel. In these embodiments, the ports150 are made using relatively short blocks 160 and leaving outfractional blocks in regular patterns to form the flow passages betweenadjacent blocks. The short blocks 160 are arranged in alternate rowswith the full blocks 164, wherein the short blocks 160 preferablyoverlap or straddle the ends of the full blocks 164 in the adjacent rowsabove and below. The short blocks 160 are arranged in size such that thespacing (width of the ports 150) between them increases from a smallestwidth in the near interval 158, to a larger width in intermediateinterval 156, and to a largest width in interval 154. In embodiments,the blocks 160, 164 may be conventional solid blocks, or may be hollowblocks, with or without tabs 730 and recesses 732 (see FIGS. 15C-15D)for interlocking.

FIG. 10 shows an arrangement of ports 200 in portions of the wall 202 atthe 3-column, 3-row near interval 208 adjacent an open (exit) end of thetunnel, a similar intermediate interval 206, and a similar far interval204 adjacent a closed end of the tunnel. In these embodiments, the ports200 comprise through openings 210 having a generally circular profilewhich comprise the flow passages formed in a central region of theblocks 212, whereas the blocks 214 are imperforate. The blocks 212 withthe flow passages 210 are arranged in alternate rows with theimperforate blocks 214. The openings 210 are arranged in size such thatthe diameters increase from a smallest diameter in the near interval208, to a larger diameter in intermediate interval 206, and to a largestdiameter in interval 204. The openings 210 can be formed in the blocks212 before (predrilled or precast, e.g.), during, or after constructionof the wall 202.

In the embodiments of FIG. 11, correspondence of the last two digits inthe reference numerals indicates like correspondence with the parts orcomponents shown in FIG. 10. FIG. 11 shows an arrangement of ports 300in portions of the wall 302 at the 3-column, 3-row near interval 308adjacent an open (exit) end of the tunnel, a similar intermediateinterval 306, and a similar far interval 304 adjacent a closed end ofthe tunnel. In these embodiments, the ports 300 comprise circularopenings 310 formed in a central region of the blocks 312, and theblocks 314 are imperforate, as in FIG. 10.

The openings 310 in these embodiments, however, are of a uniform size ordiameter or profile, whereas inserts 316 have a generally planar portionor plate 318 with a matching outside diameter or other profile forreceipt in the ports 300, and variably sized flow passages 320 areformed as circular orifices in each of the inserts 316. The inserts canbe made from a heat-resistant material such as a refractory ceramic, forexample, alumina, mullite, or a combination thereof, and can be securedin the ports 300 by means of a matching and optionally interlockingprofile and/or with refractory mortar or cement. The orifices 320 arearranged in size such that the diameters increase from a smallestdiameter in the near interval 308, to a larger diameter in intermediateinterval 306, and to a largest diameter in interval 304. Theseembodiments allow the same blocks 312, 314 to be used to facilitateconstructing the wall 302 without concern for the proper placement ofthe blocks 312, which all have the same size ports 300, whereas theinserts 316 are preferably prefabricated, e.g., predrilled or precast,with the desired size(s) of orifices 320, for placement in the ports 300before, or preferably during or after the construction of the wall 302.

In some embodiments, the inserts 316 are provided in sets of standardsizes of the orifices 320, e.g., a smallest diameter of 12.7 mm (0.5in.) or 19.1 mm (0.75 in.) incremented by 3.17 mm (0.125 in.) up to 31.8(1.25 in.)-44.4 mm (1.75 in.), and then incremented by 6.35 mm (0.25in.) up to a largest diameter of 63.5 mm (2.5 in.) or 76.2 mm (3 in.).For example, in some embodiments, the inserts 316 may have the followingstandard diameters for the passage 320:

TABLE 2 Exemplary Orifice Sizes for Inserts 3.17 mm (0.125 in.) 6.35 mm(0.25 in.) Incremented Orifice Sizes Incremented Orifice sizes 19.1 mm(0.75 in.) 38.1 mm (1.5 in.) 25.4 mm (1 in.) 44.4 mm (1.75 in.) 28.6 mm(1.125 in.) 50.8 mm (2 in.) 31.8 mm (1.25 in.) 57.2 mm (2.25 in.) 34.9mm (1.375 in.) 63.5 mm (2.5 in.) 38.1 mm (1.5 in.) 69.8 mm (2.75 in.)

In the embodiments of FIG. 12, correspondence of the last two digits inthe reference numerals indicates like correspondence with the parts orcomponents shown in FIG. 11. FIG. 12 shows an arrangement of ports 400in portions of the wall 402 at the near interval 408 adjacent an open(exit) end of the tunnel, an intermediate interval 406, and a farinterval 404 adjacent a closed end of the tunnel. As in FIG. 11, theports 400 comprise circular profiles 410 formed in a central region ofthe blocks 412, but all the blocks 412 are formed with the ports 400 (noimperforate blocks or rows). As in FIG. 11, the profiles 410 are of auniform size or diameter, inserts 416 have a plate 418 with a matchingoutside diameter or other profile for receipt in the ports 400, andvariably sized orifices 420 arranged in size such that the diametersincrease from a smallest diameter in the near interval 408, to a largerdiameter in intermediate interval 406, and to a largest diameter ininterval 404. The inserts 416 can have a range of “standard sizes” forthe orifices 420 as in Table 2, e.g., provided as an inventory of setsof inserts of each standard size.

In the embodiments of FIG. 13, correspondence of the last two digits inthe reference numerals indicates like correspondence with the parts orcomponents shown in FIG. 12. FIG. 13 shows an arrangement ofnon-circular ports 500, e.g., a rectangular or square profile, inportions of the wall 502 at the near interval 508 adjacent an open(exit) end of the tunnel, an intermediate interval 506, and a farinterval 504 adjacent a closed end of the tunnel. The square orrectangular ports 500 are formed in a central region of the blocks 512.As in FIG. 12, the ports 500 are of a uniform size, inserts 516 have aplate 518 with a matching profile for receipt in the ports 500, andvariably sized orifices 520 arranged in size such that the diametersincrease from a smallest diameter in the near interval 508, to a largerdiameter in intermediate interval 506, and to a largest diameter ininterval 504. The inserts 516 can have a range of standard sizes for theorifices 520 as in the example of Table 2.

In the embodiments of FIG. 14, correspondence of the last two digits inthe reference numerals indicates like correspondence with the parts orcomponents shown in FIG. 11. FIG. 14 shows an arrangement of ports 600in portions of the wall 602 at the near interval 608 adjacent an open(exit) end of the tunnel, an intermediate interval 606, and a farinterval 604 adjacent a closed end of the tunnel. As in FIG. 11, theports 600 comprise circular profiles 610 formed in a central region ofthe blocks 612, but in each row every third block 614 is imperforate inan offset pattern. As in FIG. 11, the profiles 610 are of a uniform sizeor diameter, inserts 616 have a plate 618 with a matching outsidediameter or other profile for receipt in the ports 600, and variablysized orifices 620 arranged in size such that the diameters increasefrom a smallest diameter in the near interval 608, to a larger diameterin intermediate interval 606, and to a largest diameter in interval 604.The inserts 616 can again have a range of standard sizes for theorifices 620 as in the example of Table 2.

In the embodiments of FIGS. 15A-15B, correspondence of the last twodigits in the reference numerals indicates like correspondence with theparts or components shown in FIG. 14. FIGS. 15A-15B show an arrangementof ports 700 in portions of the wall 702 at the near interval 708adjacent an open (exit) end of the tunnel, an intermediate interval 706,and a far interval 704 adjacent a closed end of the tunnel. The ports700 have a semicircular profile and there are two ports formed in eachblock 712, one in each half aligned horizontally such that in theconstructed wall 702 the ports are arranged in rows corresponding to therows of blocks 712 and columns corresponding to the overlapping halvesof the stacked blocks 712.

As in FIG. 14, the ports 700 in FIG. 15A are of a uniform size orprofile, inserts 716 have a plate 718 with a matching outside perimeterprofile for receipt in the ports 700, and variably sized orifices 720arranged in size such that the diameters increase from a smallestdiameter in the near interval 708, to a larger diameter in intermediateinterval 706, and to a largest diameter in interval 704. The inserts 716can have a range of standard sizes for the orifices 720 as in Table 2.The intervals 704, 706, 708 can comprise a single column of ports 700,or multiple columns. Moreover, the sizes of the orifices in any intervalor column can be different to adjust the overall flow conductivityand/or flue gas flow rate as desired, e.g., where orifices of all onestandard size would provide too much or too little flow area, theorifice sizes can be mixed such as by selecting one or more larger orsmaller orifice sizes to obtain the nearest approximation of the desiredflow area, i.e., mixing and matching from the available orifice sizes.In general, it is desired to use orifice sizes in each interval that arenot radically different in order to avoid introducing relatively moreflue gas in some areas of the interval or column, e.g., using only 2 or3 different orifice sizes that are all adjacent in the series of sizes,such as mixing 34.9 mm and 38.1 mm orifices in the same interval, ratherthan 28.6 mm and 38.1 mm orifices, for example. In some embodiments,each interval has no more than 3 different orifice sizes, or no morethan 2 different orifice sizes, or only 1 orifice size.

FIG. 15B is similar to FIG. 15A except that alternate columns of theports 700 are fitted with one or more plugs 722, which may beimperforate or undrilled versions of the inserts 716, where it may bedesired to remove ports or otherwise adjust the layout pattern of theports. In some embodiments, some of the plugs 722 are used to provideattachment points for tie rods.

FIGS. 15C-15D show an interlocking, stackable refractory block 712 withpreformed ports 700 which can be used to construct the wall 702 in FIGS.15A-15B. The block 712 can have tabs 730 on an upper surface which canbe received in a corresponding recess 732 formed in a lower portion ofthe block 712 for overlapped stacking, e.g., tabs 730 from adjacentblocks can fit into respective sides of the same recess 732 of a block712 stacked on top and overlapping the tabs of the adjacent blocks asbest seen in FIG. 15D.

With reference to FIG. 16A, in some embodiments the ports 800 in thewalls 802 may be fitted with directional flow diverters 850 to promotecirculation within the tunnel 842, e.g., to facilitate mixing of theflue gas with a reducing agent such as ammonia or urea solutionintroduced into the tunnel 842 via spray nozzle 852, which may belocated at the closed end 854 of the tunnel. The reducing agentfacilitates lower NOx emissions using a selective non-catalyticreduction technique, and improved mixing achieved by the flow diverters850 can increase mixing and thus increase residence time in the tunneland efficiency of contact between the disassociated reducing agent andany NOx contained in the flue gas. The counterclockwise-clockwise mixedflow pattern 855 indicated in FIG. 16A develops when the diverters 850direct the entering flue gas 856 down (or up) on either side, and thusup (or down) in the middle.

In the arrangement shown in FIG. 16B as another example, the flowdiverters 850 are pointed with the diverters 850 on the left sidedirecting the entering flue gas 856 down, and up on the right side, toeffect a circular circulation pattern 858.

As a further alternative demonstrating another circulating effect bychanging the direction of the diverters 850, e.g., they can be pointedhorizontally or at an angle toward the closed end 854 to promote backmixing. A back-mixing entry configuration (not shown) of the flowdiverters 850 may include accommodation for the effect of any velocitypressure or venturi translation into the pressure drop calculations forflue gas entry into the ports 800.

FIG. 17 shows an embodiment of a flow diverter 850 provided in the formof an insert 816 having a hemispherical diverter portion 860 formed withan opening 862 at the end of a sleeve 864 on the outlet side. Anenlarged sleeve portion 866 provides annular surface 868 to abut againsta lip in the port, and can help locate and stabilize the insert 816 inthe port, e.g., where the port has a profile such as an inside diametermatching that of the outside diameter or other profile of the enlargedsleeve portion 866. If desired, all or selected ones of the insert 816can also be provided with an orifice to control the flue gas entry intothe tunnel 842, as in any of FIGS. 10-15C. The flow diverter 850 can bemade from a heat-resistant material such as a refractory ceramic, forexample, alumina, mullite, or a combination thereof, and can be securedin the ports 300 by means of a matching and optionally interlockingprofile and/or with refractory mortar or cement.

EMBODIMENTS LISTING

In some aspects, the disclosure herein relates generally to furnace fluegas tunnels and related methods according to the following Embodiments,among others:

Embodiment 1

A furnace tunnel defining a flow channel for flue gas from a firebox topass to an open end of the tunnel, comprising:

a longitudinal refractory structure separating the flow channel from thefirebox;

a plurality of ports formed in the refractory structure for the flue gasto enter the flow channel from the firebox;

a regular spacing pattern of the ports along the length of therefractory structure; and

a passage through each of the respective ports providing relativelyvaried flow conductivities to control flue gas entry into the flowchannel.

Embodiment 2

The furnace tunnel of Embodiment 1 wherein the refractory structurecomprises at least one upright wall and a roof.

Embodiment 3

The furnace tunnel of Embodiment 1 or Embodiment 2 wherein therefractory structure comprises at least one upright wall comprising theports and an essentially imperforate roof.

Embodiment 4

The furnace tunnel of any one of Embodiments 1-3 wherein the refractorystructure comprises interlocking blocks.

Embodiment 5

The furnace tunnel of any one of Embodiments 1-4 wherein the refractorystructure comprises blocks, wherein the ports are integrally formed inthe blocks, and wherein perforated inserts are received in the ports,wherein the perforations define cross-sectional flow areas through therespective passages.

Embodiment 6

The furnace tunnel of any one of Embodiments 1-5 wherein the ports havea uniform profile and receive perforated inserts having a matchingprofile, and wherein the perforations in some of the inserts have across-sectional flow area that is greater with respect to theperforations of some of the other inserts.

Embodiment 7

The furnace tunnel of any one of Embodiments 1-6 wherein the ports havea uniform profile and receive perforated inserts having a matchingprofile, wherein the perforated inserts comprise sets of a plurality ofthe inserts, wherein the perforations within each set of inserts have auniform cross-sectional flow area that differs with respect to the otherone or more sets of inserts.

Embodiment 8

The furnace tunnel of any one of Embodiments 1-7 wherein the ports aredisposed in a plurality of intervals comprising a near interval adjacentto the open end, a far interval spaced away from the open end, and aplurality of intermediate intervals between the near and far intervals,wherein the passages through the ports provide the far interval with anoverall flue gas flow conductivity relatively greater than the overallflue gas flow conductivity of the near interval, and wherein the overallflue gas flow conductivities of the respective intermediate intervalsincrease successively from the near interval to the far interval.

Embodiment 9

The furnace tunnel of any one of Embodiments 1-8 wherein the ports aredisposed in a plurality of intervals comprising a near interval adjacentto the open end, a far interval spaced away from the open end, and aplurality of intermediate intervals between the near and far intervals,wherein the passages through the ports provide the far interval with anoverall cross sectional flow area greater than the overall crosssectional flow area of the near interval, and wherein the overall crosssectional flow area of the respective intermediate intervals increasesuccessively from the near interval to the far interval.

Embodiment 10

The furnace tunnel of any one of Embodiments 1-9, wherein:

the ports are disposed in a plurality of intervals comprising a nearinterval adjacent to the open end, a far interval spaced away from theopen end, and a plurality of intermediate intervals between the near andfar intervals;

each of the near, far and intermediate intervals have the same number ofports;

the ports have a uniform profile and receive perforated inserts having amatching profile; wherein the perforated inserts comprise one or moresets of the inserts having a uniform perforation diameter;

wherein the far interval has an overall cross sectional flow areagreater than the overall cross sectional flow area of the near interval,and the overall cross sectional flow area of the respective intermediateintervals increase successively from the near interval to the farinterval.

Embodiment 11

The furnace tunnel of any one of Embodiments 1-10 wherein the inserts ineach interval comprise inserts from a single set of inserts or from aplurality of different sets.

Embodiment 12

A furnace comprising a firebox and the furnace tunnel of any one ofEmbodiments 1-11.

Embodiment 13

A furnace tunnel assembly system comprising:

a plurality of interlocking refractory blocks adapted to form alongitudinal wall of a flue gas flow channel in a firebox;

at least some of the blocks comprising ports formed for the flue gas toenter the flow channel from the firebox;

respective flow passages for the ports, wherein at least some of theports comprise passages having a relatively different flow conductivitythan at least some of the other passages.

Embodiment 14

The furnace tunnel assembly system of Embodiment 13 wherein the flowpassages comprise bores through the blocks and the different flowconductivities correspond to different diameters of the bores.

Embodiment 15

The furnace tunnel assembly system of Embodiment 13 or Embodiment 14wherein the flow passages comprise orifices formed in respective insertsreceivable in the ports, wherein the different flow conductivitiescorrespond to different diameters of the orifices.

Embodiment 16

The furnace tunnel assembly system of and one of Embodiments 13-15,further comprising a plurality of sets of the inserts, wherein theinserts within each set have respective orifices of the same size, andwherein each set has different orifice sizes than the other sets.

Embodiment 17

A method comprising assembling a furnace tunnel from the blocks and orinserts of the furnace tunnel assembly system of any one of Embodiments13 to 16.

Embodiment 18

A method comprising:

stacking refractory blocks to form a longitudinal wall of a furnacetunnel;

providing a uniform density of ports in successive intervals in the wallbetween open and closed ends of the tunnel; and

providing flow passages of varying relative flow conductivity throughthe ports.

Embodiment 19

The method of Embodiment 18 further comprising placing perforatedinserts in the ports, wherein the flow passages comprise one or moreorifices formed in respective inserts receivable in the ports, whereinthe different flow conductivities correspond to different diameters ofthe orifices.

Embodiment 20

The method of Embodiment 18 or Embodiment 19 further comprising varyingcross-sectional areas of the passages to regulate entry of flue gas froma firebox into the tunnel such that a mass flow of the flue gas from thefirebox is uniformly distributed through each interval.

Embodiment 21

A method comprising:

passing flue gas from a firebox through a longitudinal refractorystructure of a tunnel; positioning passages in respective ports evenlydistributed along the length of the refractory structure to admit theflue gas into a flow channel in the tunnel; and

controlling relative flow rates of the flue gas through the ports byproviding some of the passages with a different flow conductivityrelative to the other passages.

Embodiment 22

The method of Embodiment 21, further comprising dividing the length ofthe refractory structure into a plurality of regular intervals havingthe same number of ports, wherein the overall flow conductivity of someof the intervals is different relative to the other intervals.

Embodiment 23

The method of Embodiment 21 or Embodiment 22 further comprising dividingthe length of the refractory structure into a plurality of regularintervals having the same number of ports, wherein the overall flowconductivity of successive intervals increases from a near intervaladjacent to an open end of the tunnel to a far interval adjacent aclosed end of the tunnel.

Embodiment 24

The method of any one of Embodiments 21-23, further comprising dividingthe length of the refractory structure into a plurality of regularintervals having the same number of ports, and evenly distributing amass flow rate of the flue gas entering the tunnel among the intervalssuch that the mass flow rate of the flue gas through each interval is nomore than 2% greater or less than an overall average of the mass flowrate through the intervals.

Embodiment 25

The method of any one of Embodiments 21-24, further comprising placinginserts in respective ports, the inserts comprising the respectivepassages.

Embodiment 26

The method of any one of Embodiments 21-25 wherein the inserts and portshave matching profiles.

Embodiment 27

The method of any one of Embodiments 21-26, wherein the inserts comprisesets of perforated inserts, wherein the perforations within each set ofinserts have a uniform cross-sectional flow area that differs withrespect to the other one or more sets of inserts.

Embodiment 28

The method of any one of Embodiments 21-27, further comprising dividingthe length of the refractory structure into a plurality of regularintervals having the same number of ports, wherein the intervalscomprise a near interval adjacent to an open end of the tunnel, a farinterval spaced away from the open end, and a plurality of intermediateintervals between the near and far intervals, wherein the perforationsin the inserts provide the far interval with an overall cross sectionalflow area relatively greater than the overall cross sectional flow areaof the near interval, and wherein the overall cross sectional flow areaof the respective intermediate intervals increase successively from thenear interval to the far interval.

Embodiment 29

The method of any one of Embodiments 21-28, wherein the inserts in eachinterval comprise inserts from a single set of inserts or from aplurality of different sets.

Embodiment 30

A flue gas tunnel comprising:

a longitudinal wall extending along a flow channel from a closed end ofthe tunnel to an open end of the tunnel;

a plurality of ports of uniform profile formed in the wall for the fluegas to enter the flow channel and arranged in columns from a near columnadjacent the open end to a far column adjacent the closed end and aplurality of intermediate columns between the near and far columns,wherein each of the columns has the same number of ports;

a like plurality of inserts having a profile matching the respectiveports and received therein;

orifices formed in the respective inserts;

a plurality of sets of the inserts, each set having a different orificediameter with respect to the other sets, each set of inserts comprisingorifices of uniform diameter within the set;

wherein each column comprises a plurality of inserts selected from oneor more of the sets of inserts, such that an overall cross-sectionalflow area through the orifices of each column increases from the nearcolumn to the far column.

Embodiment 31

The flue gas tunnel of Embodiment 30, wherein the wall comprisesinterlocking blocks.

Embodiment 32

The flue gas tunnel of Embodiment 30 or Embodiment 31, wherein the portsare arranged in regular rows and columns.

Embodiment 33

The flue gas tunnel of any one of Embodiments 30-32, wherein the portsare arranged in a triangular pattern or a square pattern.

Embodiment 34

The flue gas tunnel of any one of Embodiments 30-33, further comprisingsingle ones of the inserts having a different orifice diameter than thesets of the inserts in the ports of one or more of the columns.

Embodiment 35

The furnace tunnel of any one of Embodiments 1-11, further comprisingone or more directional flow diverters fitted in the ports to promoteflue gas circulation in the tunnel.

Embodiment 36

The furnace tunnel assembly system of any one of Embodiments 13-16,further comprising one or more directional flow diverters for the portsto promote flue gas circulation in the tunnel.

Embodiment 37

The flue gas tunnel of any one of Embodiments 30-34, further comprisingone or more directional flow diverters fitted in the ports to promoteflue gas circulation in the tunnel.

Embodiment 38

A furnace tunnel defining a flow channel for flue gas from a firebox topass to an open end of the tunnel, comprising:

a longitudinal refractory structure separating the flow channel from thefirebox; ports formed in the refractory structure for the flue gas toenter the flow channel from the firebox; and

directional flow diverters fitted in the ports to promote flue gascirculation in the tunnel.

Embodiment 39

The furnace tunnel of Embodiment 38, further comprising a spray nozzleto introduce a reducing agent.

Embodiment 40

The furnace tunnel of Embodiment 39, wherein the reducing agentcomprises ammonia or urea solution.

Embodiment 41

The furnace tunnel of Embodiment 38 or Embodiment 39, wherein the spraynozzle is located at a closed end of the tunnel.

Embodiment 42

The furnace tunnel of any one of Embodiments 38-41, wherein the flowdiverters comprise inserts in the ports having a diverter on an outletend.

Embodiment 43

The furnace tunnel of Embodiment 42, wherein the diverter ishemispherical.

Embodiment 44

The furnace tunnel of Embodiment 42 or Embodiment 43, wherein theinserts have a profile matching a profile of the ports.

Embodiment 45

The furnace tunnel of any one of Embodiments 42-44, wherein the insertsare provided with orifices to control flue gas entry into the tunnel.

Embodiment 46

The furnace tunnel of any one of Embodiments 42-45, wherein the insertscomprise a refractory material.

Embodiment 47

The furnace tunnel of any one of Embodiments 38-46, wherein therefractory structure comprises first and second opposing walls on eitherside of the flow channel.

Embodiment 48

The furnace tunnel of Embodiment 47, wherein the flow diverters directthe flow down on the first wall and up on the second wall to effect acircular circulation pattern.

Embodiment 49

The furnace tunnel of Embodiment 47, wherein the flow diverters directthe flow on both of the first wall and the second wall in the samedirection up or down to effect a counterclockwise-clockwise mixed flowpattern.

Embodiment 50

The furnace tunnel of Embodiment 47, wherein the flow diverters arepointed horizontally or at an angle toward a closed end of the tunnel.

Embodiment 51

A furnace tunnel defining a flow channel for flue gas from a firebox topass to an open end of the tunnel, comprising:

a longitudinal refractory structure separating the flow channel from thefirebox;

ports formed in the refractory structure for the flue gas to enter theflow channel from the firebox;

directional flow diverters comprising inserts fitted in the ports havinga diverter on an outlet end to promote circular,counterclockwise-clockwise, or backmixing flue gas circulation in thetunnel;

orifices provided in the inserts to control flue gas entry into thetunnel; a spray nozzle located at a closed end of the tunnel tointroduce a reducing agent.

Embodiment 52

The furnace tunnel of any one of Embodiments 38-51, further comprising apassage through each of the respective ports providing relatively variedflow conductivities to control flue gas entry into the flow channel.

Embodiment 53

A method, comprising:

passing flue gas from a firebox through a longitudinal refractorystructure of a tunnel;

positioning passages in respective ports evenly distributed along thelength of the refractory structure to admit the flue gas into a flowchannel in the tunnel; and

fitting directional flow diverters in the ports to promote flue gascirculation in the tunnel.

Embodiment 54

The method of Embodiment 53 or Embodiment 62, further comprisingintroducing a reducing agent into the tunnel to lower NOx emissions.

Embodiment 55

The method of Embodiment 54, wherein the reducing agent comprisesammonia or urea solution.

Embodiment 56

The method of Embodiment 54 or Embodiment 55, comprising introducing thereducing agent at a closed end of the tunnel.

Embodiment 57

The method of any one of Embodiments 53-56 or 62, comprising providingorifices in the directional flow diverters to control flue gas entryinto the tunnel.

Embodiment 58

method of any one of Embodiments 53-57 or 62, wherein the directionalflow diverters effect a circular circulation pattern in the tunnel.

Embodiment 59

The method of any one of Embodiments 53-57 or 62, wherein thedirectional flow diverters effect a counterclockwise-clockwise mixedflow pattern.

Embodiment 60

The method of any one of Embodiments 53-57 or 62, wherein thedirectional flow diverters promote back mixing in the tunnel.

Embodiment 61

The method of any one of Embodiments 53-60, further comprisingcontrolling relative flow rates of the flue gas through the ports byproviding some of the passages with a different flow conductivityrelative to the other passages.

Embodiment 62

The method of any one of Embodiments 21-29, further comprising fittingdirectional flow diverters in the ports to promote flue gas circulationin the tunnel.

Example

FIGS. 18A-18B show an example of a design for an interior tunnel wall900 of a steam-methane reformer according to the present invention,using the orifice sizes of Table 3 for inserts in 22.86 cm (9″) by 45.72cm (18″) blocks with 2 inserted orifices in each block. In this example,the tunnel is 29 m long and 3.05 m high, using 5 rows of blocks 902 withinserts over 1 row of solid blocks 904 on the floor of the furnace. Thetunnel wall 900 is 30 blocks long including 56 1-column intervals ofinserted orifices at 2 per length of the block 902, and 1 solid block (2columns of overlapping half-blocks) at either end. The intervals 1 to 26numbering from the closed end of the tunnel are shown in FIG. 18A, andintervals 27 to 56 approaching the open end in FIG. 18B. The inserts inthe blocks 902 are designated A through L in FIGS. 18A-18B according todecreasing size as shown in Table 3.

TABLE 3 Standard Orifice Sizes for Inserts in Example of FIGs. 18A-18BLetter Orifice size, mm designation (in.) A 69.8 (2.75) B 63.5 (2.5) C57.2 (2.25) D 50.8 (2) E 57.6 (1.875) F 44.4 (1.75) G 41.3 (1.625) H38.1 (1.5) I 34.9 (1.375) J 31.8 (1.25) K 28.6 (1.125) L 25.4 (1)

TABLE 4 Interval Configuration in Example of FIG. 18A-18B Total IntervalOrifices Total flow Interval Orifices flow area, (1-28) used area, cm²(in.²) (29-56) used cm² (in.²) 1 10 A 383 (59.4) 29 4 F; 6 G  142(22.06) 2 8 A; 2 B 368 (57.33) 30 2 F; 8 G  137 (21.4) 3 6 A; 4 B 355(55.27) 31 10 G  133 (20.74) 4 4 A; 6 B 341 (53.21) 32 8 G; 2 H  129(20.13) 5 2 A; 8 B 328 (51.15) 33 6 G; 4 H  125 (19.51) 6 10 B 315(49.09) 34 4 G; 6 H  121 (18.9) 7 8 B; 2 C 303 (47.22) 35 2 G; 8 H  117(18.29) 8 6 B; 4 C 291 (45.36) 36 10 H  113 (17.67) 9 4 B; 6 C 279(43.49) 37 8 H; 2 I  110 (17.11) 10 2 B; 8 C 267 (41.63) 38 6 H; 4 I 106 (16.54) 11 10 C 255 (39.76) 39 4 H; 6 I  103 (15.98) 12 8 C; 2 D244 (38.09) 40 2 H; 8 I 98.9 (15.41) 13 6 C; 4 D 234 (36.42) 41 10 I95.3 (14.85) 14 4 C; 6 D 223 (34.75) 42 8 I; 2 J 91.9 (14.33) 15 2 C; 8D 212 (33.08) 43 6 I; 4 J 88.7 (13.82) 16 10 D 202 (31.42) 44 4 I; 6 J85.3 (13.3) 17 8 D; 2 E 197 (30.66) 45 2 I; 8 J 82.1 (12.79) 18 6 D; 4 E192 (29.89) 46 10 J 78.7 (12.27) 19 4 D; 6 E 187 (29.13) 47 8 J; 2 K75.8 (11.81) 20 2 D; 8 E 182 (28.37) 48 6 J; 4 K 72.8 (11.34) 21 10 E177 (27.61) 49 4 J; 6 K 69.7 (10.87) 22 8 E; 2 F 173 (26.9) 50 2 J; 8 K66.8 (10.41) 23 6 E; 4 F 168 (26.19) 51 10 K 63.8 (9.94) 24 4 E; 6 F 163(25.48) 52 8 K; 2 L 61.1 (9.52) 25 2 E; 8 F 159 (24.76) 53 6 K; 4 L 58.4(9.11) 26 10 F 154 (24.05) 54 4 K; 6 L 55.8 (8.69) 27 8 F; 2 G 150(23.39) 55 2 K; 8 L 64.9 (8.27) 28 6 F; 4 G 146 (22.73) 56 10 L 50.6(7.85)

The intervals are labeled 1 to 56 at the top of the wall 900, whereinterval 1 is near the closed end 906 and interval 56 is near the openend 908. The size of the orifices used in each block is indicatedschematically in FIG. 18 by the letter A to L according to Table 3. Thenumber of orifices of each size used in each interval (both walls) andthe total flow area of each interval (both walls) is given in Table 4.

In this example, the overall flue gas flow conductivity of each intervalis adjusted by adjusting the cross-sectional flow area using orificesfrom 1 or 2 sets of the available orifice sizes in each column, e.g.,interval 1 uses 10 (5 in each wall of the interior tunnel) of theinserts with the “A” orifices, interval 2 uses 8 A's and 2 B's, and soon. The smaller orifices in each interval are placed ascending in thelower rows to direct less of the flue gas to the lower rows,corresponding to the temperature-sensitive lower ends of the reactortubes.

Although only a few exemplary embodiments have been described in detailabove, those skilled in the art will readily appreciate that manymodifications are possible in the example embodiments without materiallydeparting from this disclosure. For example, any embodimentsspecifically described may be used in any combination or permutationwith any other specific embodiments described herein. Accordingly, allsuch modifications are intended to be included within the scope of thisdisclosure as defined in the following claims. In the claims,means-plus-function clauses are intended to cover the structuresdescribed herein as performing the recited function and not onlystructural equivalents, but also equivalent structures. Thus, although anail and a screw may not be structural equivalents in that a nailemploys a cylindrical surface to secure wooden parts together, whereas ascrew employs a helical surface, in the environment of fastening woodenparts, a nail and a screw may be equivalent structures. It is theexpress intention of the applicant not to invoke 35 U.S.C. § 112(f) forany limitations of any of the claims herein, except for those in whichthe claim expressly uses the words ‘means for’ or ‘step for’ togetherwith an associated function without the recitation of structure.

What is claimed is:
 1. A furnace tunnel assembly system comprising: aplurality of interlocking refractory blocks adapted to form alongitudinal wall of a flue gas flow channel in a firebox; at least someof the blocks comprising ports integrally formed therein, wherein theports are arranged in regular rows and columns; and inserts for theports, wherein at least some of the inserts comprise plugs comprisingimperforate plates having a profile matching the ports to inhibit fluegas entry from the firebox to the flow channel, and wherein some of theports comprise flow passages for the flue gas to enter the flow channelfrom the firebox.
 2. The furnace tunnel assembly system of claim 1,further comprising tie rods.
 3. The furnace tunnel assembly system ofclaim 2, wherein some of the plugs provide attachment points for the tierods.
 4. The furnace tunnel assembly system of claim 1, furthercomprising: wherein at least some of the flow passages have a relativelydifferent flow conductivity than at least some of the other flowpassages; and wherein the different flow conductivities are provided tocontrol flue gas entry into the flow channel.
 5. The furnace tunnelassembly system of claim 4, wherein some of the inserts compriseperforated plates having a profile matching the ports.
 6. The furnacetunnel assembly system of claim 5, wherein the perforations in some ofthe perforated plates have a cross-sectional flow area that is greaterwith respect to the perforations of some of the other perforated plates.7. The furnace tunnel assembly system of claim 6, wherein the perforatedplates comprise sets of a plurality of the perforated plates, whereinthe perforations within each set of perforated plates have a uniformcross-sectional flow area that differs with respect to the other one ormore sets of perforated plates.
 8. The furnace tunnel assembly system ofclaim 7, wherein the ports are disposed in a plurality of intervalscomprising a near interval adjacent to an open end of the flow channel,a far interval spaced away from the open end, and a plurality ofintermediate intervals between the near and far intervals, wherein thepassages through the ports provide the far interval with an overall fluegas flow conductivity relatively greater than the overall flue gas flowconductivity of the near interval, and wherein the overall flue gas flowconductivities of the respective intermediate intervals increasesuccessively from the near interval to the far interval.
 9. The furnacetunnel assembly system of claim 8, wherein a mass flow rate of the fluegas through each interval is no more than 2% greater or less than anoverall average of the mass flow rate through the intervals.
 10. Thefurnace tunnel assembly system of claim 1, wherein the ports aredisposed in a plurality of intervals comprising a near interval adjacentto an open end of the flow channel, a far interval spaced away from theopen end, and a plurality of intermediate intervals between the near andfar intervals, wherein the flow passages through the ports provide thefar interval with an overall cross sectional flow area greater than theoverall cross sectional flow area of the near interval, and wherein theoverall cross sectional flow areas of the respective intermediateintervals increase successively from the near interval to the farinterval, and wherein a mass flow rate of the flue gas through eachinterval is no more than 2% greater or less than an overall average ofthe mass flow rate through the intervals.
 11. The furnace tunnelassembly system of claim 1, further comprising: wherein the ports aredisposed in a plurality of intervals comprising a near interval adjacentto the open end, a far interval spaced away from the open end, and aplurality of intermediate intervals between the near and far intervals;wherein each of the near, far and intermediate intervals have the samenumber of ports; wherein the ports have a uniform profile and receiverespective plugs or perforated plates having a matching profile; whereinthe perforated plates comprise one or more sets of the perforated plateshaving a uniform perforation diameter; wherein the far interval has anoverall cross sectional flow area greater than the overall crosssectional flow area of the near interval, and the overall crosssectional flow areas of the respective intermediate intervals increasesuccessively from the near interval to the far interval.
 12. The furnacetunnel assembly system of claim 11 wherein the perforated plates in eachinterval comprise perforated plates from a plurality of different sets.13. The furnace tunnel assembly system of claim 11, further comprising aplurality of sets of the perforated plates, wherein the perforatedplates within each set have respective perforations of the same size,and wherein each set has different perforation sizes than the othersets.
 14. The furnace tunnel assembly system of claim 11, wherein theports are arranged in regular rows and columns.
 15. The furnace tunnelassembly system of claim 14, wherein the ports are arranged in atriangular pattern or a square pattern.
 16. A furnace tunnel assemblysystem comprising: a plurality of interlocking refractory blocks adaptedto form a longitudinal wall of a flue gas flow channel in a firebox; atleast some of the blocks comprising ports formed therein, wherein theports are arranged in regular rows and columns; and respective insertsfor the ports, wherein at least some of the inserts comprise plugscomprising imperforate plates, and wherein some of the inserts compriseperforated plates.
 17. The furnace tunnel assembly system of claim 16wherein the ports are disposed in a plurality of intervals comprising anear interval adjacent to an open end of the flow channel, a farinterval spaced away from the open end, and a plurality of intermediateintervals between the near and far intervals, wherein the perforationsprovide the far interval with an overall cross sectional flow areagreater than the overall cross sectional flow area of the near interval,and wherein the overall cross sectional flow areas of the respectiveintermediate intervals increase successively from the near interval tothe far interval.
 18. The furnace tunnel assembly system of claim 17,wherein a mass flow rate of the flue gas through each interval is nomore than 2% greater or less than an overall average of the mass flowrate through the intervals.
 19. A furnace comprising a firebox and afurnace tunnel assembled from the furnace tunnel assembly system ofclaim
 1. 20. A furnace comprising a firebox and a furnace tunnelassembled from the furnace tunnel assembly system of claim
 16. 21. Amethod comprising assembling a furnace tunnel from the blocks andinserts of claim
 1. 22. A method comprising assembling a furnace tunnelfrom the blocks, inserts, and tie rods of claim
 16. 23. A methodcomprising: positioning a plurality of interlocking refractory blocks toform a longitudinal wall of a flue gas flow channel in a firebox,wherein at least some of the blocks comprising ports integrally formedtherein; arranging the ports in regular rows and columns; plugging someof the ports with plugs comprising imperforate plates having a profilematching the ports to inhibit flue gas entry from the firebox to theflow channel; and providing some of the ports with flow passages for theflue gas to enter the flow channel from the firebox.